1. Field of the Invention
The present invention relates generally to the field of robotics and more particularly to a robot wrist having semicircular links to produce relative motion of a pair of radial arms.
2. Description of the Related Art
There are presently two types of robot wrists. The first type of robot wrists are those that are actuated ball and socket (spherical) joints as are shown in the following references.
The Humen U.S Pat. No. 3,973,469 shows a power transmission mechanism which utilizes a spherical member. The machine could be back-driven through fluid pressure to actuate a spherical joint.
The Wells U.S. Pat. No. 4,045,958 presents a hydraulically actuated multi-directional positioner which could be used as a robot wrist.
The Rosheim U.S. Pat. Nos. 4,194,437 and 4,296,681 describe hydraulic servo mechanisms which impart an arbitrary rotary movement.
The Dien U.S. Pat. No. 4,628,765 describes the use of two slotted spherical yokes in order to control the direction of a control pin which extends from the ball of a spherical joint. The control pin may serve as the roll axis of the end-effector of a robot.
All these types of robot wrists are capable of singularity free motions within the workspace of their end-effector. Their workspace is less than a hemisphere due to interference between the roll axis attached to the ball and the socket of the spherical joint.
The second type of robot wrists are those that imitate an actuated ball and socket joint with multiple actuated revolute (turning) joints as is shown in the following references.
The Ikeda U.S. Pat. No. 4,683,406 presents a joint assembly which is similar in motion to the human forehand.
The Taylor U.S. Pat. No. 4,073,201 describes a powered wrist joint containing three intersecting revolute joints. The mechanism is C-shaped permitting movement of the roll shaft about the yaw axis through an arc in excess of 180.degree..
Many wrists of the second type also incorporate gear systems to accommodate drives external to the wrist. The Rosheim U.S. Pat. No. 4,686,866 presents a non-spherical robot wrist joint having a mechanical joint for simultaneous pitch, yaw and roll movement. Within its workspace the wrist joint is singularity free.
The Kimura U.S. Pat. No. 4,574,655 incorporates three intersecting revolute joints and a system of bevel gears and shafts to accommodate drives remote of the wrist.
The Stackhouse U.S. Pat. No. 4,068,536 also describes a remotely-driven wrist mechanism containing three intersecting revolute joints. Drive is provided by three concentric shafts.
The Fletcher U.S. Pat. No. 4,068,763 presents a geared three axis robot wrist with the feature of fine positioning ability.
With the exception of Rosheim U.S. Pat. No. 4,686,866, this type of wrist encounters singularities in the wrist motion (unavoidable mechanically degenerate configurations), or interference problems between links. The Rosheim U.S. Pat. No. 4,686,866 has a nonspherical structure.
In robotics, a major problem is that of the wrist joint singularity. In order to overcome this problem, it becomes necessary to introduce redundant bodies and joints into the wrist joint. With redundancy introduced, a new problem of interference between links is encountered.